1. Field of the Invention
The present invention relates to a method that corrects and accurately detects a fully-charged battery capacity, which decreases with increasing the number of charging/discharging operation cycles.
2. Description of the Related Art
A capacity that can be charged to a fully-charged state (i.e., fully-charged capacity (Ahf) of a battery decreases with time and with increasing the number of charging/discharging operation cycles. The fully-charged capacity (Ahf) is expressed by the product of current (A) and time (h). The fully-charged capacity (Ahf) is the capacity of a battery that can be discharged from a fully-charged state to a fully-discharged state. As the battery that is fully charged is discharged, the product of current (A) and time (h) of the battery that can be discharged decreases. That is, the remaining capacity (Ahr) of the battery is getting smaller than the fully-charged capacity (Ahf. The remaining capacity (Ahr) relative to the fully-charged capacity (Ahf) is expressed as a remaining capacity (SOC [%]). The remaining capacity (SOC [%]) of the battery can be determined based on the no-load voltage (VOCV) of the battery. The reason is that the remaining capacity (SOC [%]) of the battery is detected by the no-load voltage. Since the remaining capacity (SOC [%]) is the remaining capacity (Ahr) relative to the fully-charged capacity (Ahf, even on the condition that the remaining capacity (SOC [%]) is the same value, the product of current (A) and time (h) of the battery that can be actually discharged varies. Since as the battery is repeatedly charged/discharged, the fully-charged capacity (Ahf) of the battery decreases, in order to accurately detect the remaining capacity (Ahr) of the battery, it is necessary to accurately detect the fully-charged capacity (Ahf of the battery, which decreases as the battery is repeatedly charged/discharged. The reason is that, if the fully-charged capacity (Ahf) of the battery decreases by half, even on the condition that the remaining capacity (SOC [%]) is the same value, the product of current (A) and time (h) of the battery that can be actually discharged decreases by half.
The fully-charged capacity (Ahf) of a battery can be detected by integrating charge capacity amounts that are charged to the battery in the fully-discharged state to the fully-charged state. The fully-charged capacity (Ahf) can be also detected by integrating discharge capacity amounts that are discharged from the battery in the fully-charged state to the fully-discharged state. However, batteries are unlikely to be used in the state where the batteries are fully charged from the fully-discharged state, or in the state where the batteries are fully discharged from the fully-charged state. In the most cases, batteries are charged before being fully discharged, and are not fully discharged from the fully-charged state. If a battery is not fully discharged, even when the battery is charged, the fully-charged capacity (Ahf) of the battery cannot be calculated. In order to detect the fully-charged capacity (Ahf) of this battery, it is necessary to fully discharge the battery prior to charging operation and then to fully charge the battery. In this method, the battery is required to be charged for a long time. In addition to this, this method cannot be used for a backup battery or the like that has less calculation chance.
As one method that solves these disadvantages, Japanese Patent Laid-Open Publication No. 2002-236154 discloses a method that detects the deterioration degree of a battery based on the accumulated charging capacity amount of the battery, and detects the reduction value of the fully-charged capacity (Ahf) of the battery. Also, this Publication discloses a method that detects the reduction rate of the fully-charged capacity of a battery based on the storage temperature and the remaining capacity of the battery as parameters.